The present invention relates to a wind turbine auxiliary drive system.
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft either directly drives the generator rotor or through the use of a gearbox.
Two important auxiliary systems generally provided on wind turbines are the pitch system and the yaw system. Pitch systems are employed for adapting the position of a wind turbine blade to adapt to varying wind conditions. In this respect, it is known to rotate a wind turbine blade in such a way that it generates less lift (and drag) when the wind speed increases. In this way, even though the wind speed increases, the torque transmitted by the rotor to the generator remains substantially the same. It is furthermore also known to rotate wind turbine blades towards their stall position (so as to reduce the lift on the blades) when the wind speed increases. These wind turbines are sometimes referred to as “active-stall” wind turbines. Pitching may furthermore also be used for rotation of the blade towards its vane position, when a turbine is temporarily stopped or taken out of operation for e.g. maintenance.
Pitch systems generally comprise an electric or hydraulic motor which, through the use of reduction gearing (sometimes referred to as a “reductor”, or as a “reduction drive”), drives an actuating gear. Said actuating gear meshes with an annular gear provided on the wind turbine blade to set the wind turbine blade into rotation. Other actuating mechanisms operated by a pitch motor are however also known.
It is further known to provide an individual pitch system (comprising a separate motor and separate control) for each wind turbine blade of a rotor. It is also known to provide a common pitch system wherein the pitch angle of the blades is the same for all blades on a rotor. Such a common pitch system may comprise a single motor or may comprise a plurality of motors, one for each blade.
Another example of an auxiliary drive system on a wind turbine is, as mentioned before, the yaw drive system. In a yaw drive system, generally, a plurality of (electric or hydraulic) motors with suitable reductors is used for driving gears that mesh with an annular gear attached to the nacelle or to the wind turbine tower. The nacelle can thus be rotated around the tower's longitudinal axis in or out of the wind direction. In some known wind turbines, four separate yaw motors are provided. In other known wind turbines, six separate yaw motors are provided. This plurality of yaw motors is provided for reasons of redundancy. Even if one or more yaw motors fail, the wind turbine can still be operated safely. Another benefit of providing a plurality of yaw motors is that the local wear on the annular gear may be reduced.
Periodic maintenance may require inspection of either the pitch system and/or the yaw system. Also, from time to time, components of the yaw system or pitch system may need to be replaced and/or repaired. In these instances, the wind turbine is stopped and taken out of operation. Maintenance personnel can go up the tower and carry out the planned maintenance or inspection. In principle, both the yaw motors and pitch motors are inhibited from rotating in this state by the brakes provided on these motors. However, it may still be possible for a strong wind gust to cause either a wind turbine blade and/or the nacelle to rotate slightly. This may cause a dangerous situation for the personnel carrying out the maintenance. For this reason, it is generally required in the relevant technical standards to provide additional mechanical locking systems for both these systems.
In this respect, it is known for maintenance personnel to carry a mechanical locking instrument up the tower. Said mechanical locking instrument is then temporarily mounted within the wind turbine blade in such way that the locking instrument meshes with an annular gear provided within the wind turbine blade. In this way, the blade may be securely locked in its place. A disadvantage of this sort of arrangement is that mounting (and demounting) of the locking instrument may require a substantial amount of time, which can make the maintenance more costly. Another disadvantage is that the personnel has to carry the potentially heavy locking instrument and the accompanying tools from one wind turbine to the next. It is furthermore possible for the personnel to forget some or all of the locking instrument(s) and accompanying tools so that maintenance sometimes may have to be postponed.